Polymers and copolymers of lactic acid, generally known as poly(lactic acid), slowly hydrolyze and degrade to environmentally benign products. These polymers are well behaved thermoplastics with appealing aesthetic qualities. Consequently, high molecular weight polymers (that is, those having a molecular weight of at least 10,000 and typically in the range of 15,000 to 500,000) of lactic acid are potential replacements for poly(styrene) and other non-biodegradable polymers in numerous applications, such as packaging. In addition, lactic acid has been suggested as an agent to inhibit growth of microorganisms on meats, poultry, seafood and other moisture-containing perishable items.
However, a major disadvantage of poly(lactic acid) as a packaging material is that it has relatively poor mechanical strength. Thus, while these polymers were suitable for films and the like, their lack of mechanical strength prevented their use in such applications as bottles, foamed trays, shaped containers and the like.
Epoxy plasticizers; i.e., epoxidized oils and esters, are generally known and have been shown to improve the appearance and durability of vinyl products. These plasticizers are also known to act synergistically with mixed metal stabilizers. This invention is based on the discovery that poly(lactic acid) compositions containing an epoxidized oil as a plasticizer have improved physical properties.